The present invention relates to a method and apparatus for mulching waste material and is particularly although not exclusively concerned with mulching of green organic material (GOM) for the purpose of converting that GOM into a form for composting. It will be convenient therefore to describe the invention as it relates to that application, although it should be appreciated that the invention has wider application in the mulching of various waste products.
Green organic material is an expression adopted to cover a wide range of organic waste and includes wooden waste products such as trees, branches, logs, grass cuttings, hard and croft woods and other foliage, but excludes treated wooden products. The disposal of GOM traditionally has been by way of dumping, such as into rubbish dumps or land fills, or if possible it has also been burnt off. However, in more recent years, GOM more and more is being treated to produce organic compost and the demand for such compost over recent years has steadily grown.
Australian Standard 4454/1997 governs the characteristics preferred for commercial sale of compost and that Standard covers a variety of composting systems and products. The present invention is highly suitable for producing compost through the open windrow composting system and can meet the requirements of the Standard for that system although it does have application to other composting systems.
Open windrow composting for GOM is known and normally involves treating the GOM in a manner which reduces the GOM into smaller particles and feeding the treated product to a stockpile. The product is then screened to eliminate particles which are too large for open windrow composting after which fertiliser is added and the product then windrowed. The larger particles which do not pass through the screen the first time are retreated to reduce their size and are then fertilised and windrowed as before. Most machinery manufactured for mulching GOM in the above manner has employed a hammer mechanism which applies a repetitive impact force to the GOM so as to break it down into smaller particles. The particles are collected, before being passed over sorting screens through which particles of the desired size fall. The process is continuous, so that particles which do not fall through the screens are returned for further impact treatment before again being passed over the sorting screens. The process continues until all the GOM has been converted to a size that fits through the screens. When the particles pass through the screens they fall onto a conveyor which transports the GOM to be windrowed.
A disadvantage with known mulching machines concerns the of use particle screens. Such screens are commonly clogged over time by particles that are small enough to be trapped by the screen, but which are too large to pass through. Periodic cleaning or changing of the screens is therefore required and that creates downtime for the machine. The screens also tend to limit access to the internal components of the machine, so that maintenance of the machine is made more difficult. A further disadvantage relates to the product produced by such machines, because it is not in a form which can be windrowed without further treatment. Normally, the particles are required to the treated with fertiliser prior to windrowing, to produce mulch that will adequately compost according to the requirements for commercial compost as set out in Australian Standard 4454/1997.
It is an object of the invention to overcome or at least alleviate one or more of the disadvantages of the prior art. In particular, it is an object of the invention to produce a mulch which can be windrowed immediately and preferably without further treatment. It is a further object of the invention to produce a mulch which has a controlled moisture content and particle size.
According to the present invention there is provided a method of processing green organic waste (hereafter xe2x80x9cGOMxe2x80x9d) into mulch product for forming a mulch windrow, including feeding GOM to a first cutting zone and rotating a plurality of blades through that zone to cut the GOM into smaller particles, transferring the particles to a second cutting zone and rotating a plurality of blades therethrough to reduce their size to a suitable mulch particle size and ejecting said mulch particles at high velocity to form a windrow, the method further including the addition of moisture to increase the moisture content at the windrow formed.
The present invention also provides apparatus for processing GOM to form mulch particles for a mulch windrow, said apparatus including a first cutting zone and at least one blade for rotation through said first cutting zone for cutting the GOM into particles, a second cutting zone and at least one blade for rotation through said second cutting zone for cutting said particles to reduce their size to a suitable mulch particle size, feeding means to feed GOM to said first cutting zone and ejecting means to eject said mulch particles from said second cutting zone at high velocity to form a windrow, and means to increase the moisture content of the windrow formed by adding moisture.
The invention as defined above is distinguished from the prior art, because the mulch particles produced are of a size and moisture content that readily composts when formed into a windrow. Additionally, the use of the rotating blades as opposed to impacting hammers facilitates reduction of the GOM without requiring sorting screens. The size of the particles formed by the invention is partly a function of the speed at which GOM is fed to the first cutting zone, and partly a function of the rotational velocity of the blades rotating through the respective cutting zones. GOM can be processed at quite high speed. For example the following feed speeds to the first cutting zone are appropriate
Larger material (150 mm-300 mm dia branches and twigs)xe2x88x920.125 m/s
Medium material (150 mm-150 mm dia branches and twigs)xe2x88x920.25 m/s
Small material (0.50 mm dia branches and twigs)xe2x88x920.5 m/s
For the above feeding speeds, it is preferred that the blades rotate at a high speed in the range of 1600 RPM. Within these ranges, the particle size of the GOM produced can be in the region of 0.50 mm which is an optimum size for composting.
The addition of moisture to the particles ensures that the mulch product can be produced with an optimum moisture content, preferably around 38%, conducive to composting. The moisture typically can be provided in the form of water and preferably is injected through water jets into the particles in an evenly distributed manner. The water is preferably injected into the first cutting zone, although it may be injected elsewhere. Preferably the volume of water injected can be controlled and varied as necessary, so that variations in the moisture content of the GOM prior to mulching can be accommodated. Also, the water can contain such additives as considered desirable for proper or optimum composting of the mulch formed, such as nutrients.
It is a characteristic of the known machinery and methods that they do not, and largely cannot, add water. The reason for this, is that the mulch product is delivered to form a windrow via a conveyor and that delivery does not facilitate addition of moisture. Additionally, the delivery of the particle mulch in this manner also does not result in a windrow which is of a density achievable by the method and apparatus of the invention, as will become apparent later. The deficiency in moisture content and density can seriously inhibit the microbial activity within the windrow which is essential for composting. If the windrow is left in this state for some time, it can possibly turn aerobic or anaerobic depending upon the density thereof and that could cause pH imbalance if the windrow has proceeded to that state. The method and apparatus of the invention can be used to correct this problem by re-mulching the windrow and adding correct nutrients just prior to re-mulching or by injecting water during re-mulching.
The blades which pass through the first and second cutting zones can be supported on separate blade mounting arrangements which rotate about separate axes. Preferably however, the blades are supported on a single blade mounting arrangement which is arranged so that the blades pass through both cutting zones, the zones being displaced from each other about the rotational path of the blade mounting arrangement.
The blade mounting arrangement can include any number of blades suitably arranged relative to one another and it is possible that a single blade be provided. However, it is preferred that a plurality of blades be provided and in one mounting arrangement, a cylindrical cutting mill is provided, which supports a plurality of blades extending both axially thereof and extending outwardly beyond the circumference of the mill. Separate groups of axially extending blades can be disposed of circumferentially of the mill and in a preferred arrangement, four groups of axially extending blades are spaced equidistantly about the mill circumference.
The blade or blades are preferably mounted for movement relative to the cutting mill and in one arrangement, they are rotatably mounted to the cutting mill. This ability to rotate reduces the potential for damage to occur to the blades in the event that the GOM encountered is too hard for the blade to cut, or if other GOM, such as metallic nails or rocks etc enter the cutting zones. Alternative arrangements, such as spring mounting arrangements, are also appropriate for this purpose.
The transfer of particles from the first cutting zone to the second cutting zone can occur in any suitable manner by any suitable means. In one preferred form, the blades which pass through the first cutting zone imparts a force in a direction which causes the particles to move into the second cutting zone. Thus, the angle at which the blades engage the GOM at the first cutting zone may be such as to cause the particles to be pushed toward the second cutting zone. Alternatively, or in addition to, guiding means may be employed. The guiding means may take the form of a guiding plate or plates, which direct the particles to the second cutting zone.
The ejection of particles from the apparatus can be facilitated by any suitable means. Preferably however, the blade speed through the second cutting zone is such as to impart a velocity to the particles that is sufficient for their ejection and for the creation of a windrow of desired characteristics. The velocity of the particles principally determines the density of the windrow and that velocity can be controlled by altering the rotational speed of the blades through the second cutting zone. The density of a windrow formed by the invention can be greater than that formed by conventional means and occurs principally due to the impact of mulch particles to progressively laid layers of mulch. This arrangement is distinguished from the prior art in which the mulch, once prepared and treated, is laid in a windrow, not ejected according to the invention.
Guiding means are preferably provided to guide the mulch particles in the correct manner to form a windrow. The guiding means can include a plate which directs the mulch particles in the desired direction from the second cutting zone and that plate may be flat, or curved to form a channel and may be adjustable in the direction it guides the particles. In one form, the guiding means includes a delivery chute from which the particles are delivered to form a windrow. The delivery chute can be formed to spread or to compact the mulch particles received from the second cutting zone and the chute may be adjustable to adjust the direction at which the mulch particles exit the chute.
The apparatus of the invention is preferably portable and is preferably mounted on a trailer or formed with wheels. The apparatus preferably can be trailed behind a car, truck or tractor, or includes its own motive capability, so that a windrow of some length can be progressively formed by progressive movement of the apparatus.
The method and apparatus of the invention is such as to produce mulch of a controllable moisture content which can be used to form a windrow for composting. Additionally the use of rotary blades at two separate zones results in an optimum particle sizes for composting without the need for particle screens. The preferred aspects of the invention facilitate the formation of a densely packed windrow which can be formed in a relatively easy manner. The invention therefore has significant advantages in the composting industry.